The present invention relates to neutron responsive self-powered radiation detectors. A self-powered radiation detector is one which does not require application of any potential between the electrodes of the device. Such devices are typically of a very small diameter and include a centrally disposed emitter wire, a dielectric insulator about the emitter, and a coaxial collector sheath about the dielectric insulator. The self-powered neutron detector is particularly suitable for in-core real time measurement of neutron flux. Most such self-powered neutron detectors utilize an emitter material having a high neutron capture cross-section so that beta radiation is emitted from the emitter upon neutron interaction. The emitted beta radiation passes to the collector sheath electrode. The externally sensed current results from the beta current passing from the emitter to the collector. The dielectric insulator has been thought necessary to slow down the beta particles to permit their ultimate collection by the collector sheath electrode.
For in-core instrumentation, relatively high gamma radiation is always present along with the neutron flux. The gamma radiation produces a current contribution for such self-powered detectors which detracts from the neutron sensitivity of the device. A variety of gamma compensation techniques have been utilized to permit distinction of the neutron signal from the gamma signal. For fast-neutron flux monitoring detectors, the average neutron flux cross-section is relatively low and the gamma induced current is about the same magnitude as the neutron induced current. The neutron current is induced by the outward movement of beta radiation emitted from the emitter. The external gamma environment will produce inwardly moving Compton electrons moving from the collector to the emitter. There are thus two opposed currents induced in the detector from the separate mechanisms. It is highly desirable to be able to eliminate such gamma induced current in self-power detectors, particularly for devices designed for measuring fast neutron flux.